SDI-TD-DMUX-4
Rev.
5
4
Operation
The SDI-TD-DMUX-4 board receives any combination of four 270 Mbps time division
multiplexed SD-SDI or DVB-ASI signals embedded in a 1.485 Mbps HD signal via an optical
or electrical HD interface according to SMPTE 346M-2000. An SDI-TD-MUX-4 board is
required to generate this HD-signal, normally at a remote location and linked via an optical
fibre or an electrical coax cable.
Channel swapping is available either from DIP-switches or remotely via the standard GYDA-
SC interface. All outputs can be either 270 Mbps SD-SDI or DVB-ASI (188 or 204 word
packets).
The SD-SDI clocks for each channel will be regenerated based on a frequently received SCR
counter (stream clock reference – refer to the SMPTE 346M-2000 standard). This ensures a
stable, low-jitter output.
There are four signal generators on the board. Each can be set to colour bar 525, colour bar
625, black 525 or black 625 from GYDA-SC. Since the SDI-TD-DMUX-4 does not have a local
clock reference input, a valid SD signal must be present in the HD stream from the SDI-TD-
MUX-4 (i.e. at least one SD signal must be connected to one of the SDI-TD-MUX-4 SD
inputs) in order to guarantee that the output signals from the test signal generators in the
SDI-TD-DMUX-4 are compliant with the SD clock requirements.
The signal generator will by default automatically connect to the output with a black signal
whenever the corresponding input stream is lost (when no signal available in the stream
from the SDI-TD-MUX-4 board). The format (525 vs. 625 lines) will be selected automatically
to follow the signal that was lost.
There are also two alternatives to this default behaviour for the signal generators. You can
overrun this by using the DIP-switches on the board (see section 3.1) or you can turn off the
output signal automatically on loss of input stream by setting this from GYDA-SC. If you
need this feature and your revision of GYDA-SC does not support this, ask Network
Electronics for support on this matter (this is a late feature added in May 2007).
The board measures the RSSI (Received Signal Strength Indicator) from the optical input.
Normally, the readout (in the GYDA-SC GUI) shows the signal strength to /-1-2dB.
However, the measurement is NOT calibrated to this accuracy and the readout should be
used as an indication only. Also be aware that the readout is fairly linear within a range from
-15dB to -30dB. Outside this range, the readout will show a fixed value not representative of
the actual signal level. So, when showing a signal level of -15dB or more or a signal level of -
30dB or less, then ignore the readout – just know that the signal is either strong enough
with good margins or too weak to be detectable.
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